We are billing a surgery with a -78 modifer because it was a return to the OR for a related procedure. We have been told that billing another surgery with a -78 modifer does not extend the post op period. Using this information we have the post op period ending 90 days after the original surgery. Does anyone know of a resource with documentation showing that a -78 modifier does not extend the post op period? This information is needed to appeal an insurance denial.